No it doesn’t it means that 50% of crops are grown with synthetic nitrogen that is it. Your logic is flawed because you lack understanding of how farming and global food markets work. There is not a 1 to 1 correlation between what is grown and what is consumed. The primary reason why synthetics are used is because it is easier and cheaper than using natural sources. This however does not mean that natural sources cannot be used or are not available. Farmers choose to use synthetics over practices like cover crops for fixing nitrogen for economic reasons. They will change practices for the exact same reason if they feel it is in their best interests. On top of that almost 20% of food grown across the world is lost to waste.